440 



THE DEVELOPMENT OF THE CHICK 



with the ventral posterior border of the ilium, and the pubis, 

 except at its anterior and posterior ends, with the free border 

 of the ischium. 



The spina iliaca, a pre-acetabular, bony process of the ilium, 



requires special mention in- 

 asmuch as it has been inter- 

 preted (by Marsh) as the 

 true pubis of birds, and the 

 element ordinarily named 

 the pubis as homologous to 

 the post-pubis of some rep- 

 tiles. There is no evidence 

 for this in the development. 

 The spina iliaca develops as 

 a cartilaginous outgrowth of 

 the ilium and ossifies from 

 the latter, not from an inde- 

 pendent center (Mehnert). 



The Leg-skeleton. The 

 skeleton of the leg develops 

 from the axial mesenchyme, 

 which is at first continuous 

 with the primordium of the 

 pelvic girdle. In the process 

 FIG. 249. Photograph of the skeleton of chondrification it seg- 

 of the leg of a chick embryo of 15 days' ments i n t o a larger number 

 icubation Prepared by the potash Qf elementg than found in 

 method. (Preparation and photograph ,. , . . . 



by Roy L. Moodie.) ^ ne adult, some of which are 



1, Tibia. 2, Fibula. 3, Patella. 4, suppressed and others fuse 



9, Tarsal ossification. 10, Second, third ou t from the palate-like ex- 



SiS^iPm'TV^ /L First metal pansion of the primitive 



tarsal. 1, II, III, IV, First, second, third, f. 



and fourth digits. limb in the same fashion as 



in the wing. In general the 



separate elements arise in the proximo-distal order (Figs. 242 and 

 249). 



The femur requires no special description; ossification begins 

 on the ninth day. 



The primordium of the fibula is from the first more slender 

 than that of the tibia, though relatively far larger than the adult 



